Phenological and genetic characterization of Sedum hispanicum (Crassulaceae) in the Italian peninsula at the western margin of its distribution

Background and aims – Sedum hispanicum acts as a pioneer species on the gypsum outcrops of Emilia Romagna region (Northern Italy). The species was studied in two Sites of Community Importance through a comparative phenological and genetic diversity analysis to provide insights into strategies adopted by the species for successful reproduction in the harsh conditions of these rocky outcrops. Methods – Phenology was examined in individuals from four sampling sites chosen in one study area (Gessi Bolognesi e Calanchi dell’Abbadessa, GB) from March to June in two years (2013 and 2015) with different spring temperatures. Reproductive and vegetative phenophases were compared among sites and over years. ISSR-based molecular analysis was performed to obtain genetic diversity measures on individuals collected at the same four GB sites and, for comparison, in a second area (Gessi di Monte Rocca, Monte Capra e Tizzano). Key results – Individuals at the four GB sites showed inter-annual differences in full flowering and leaf senescence, but intra-annual synchrony of all monitored phenophases. Moderate amounts of genetic diversity were observed in the two areas (P% = 79.67, 67.48; I = 0.209, 0.205; He = 0.118, 0.122). Low genetic structure (Φst = 0.05; Gst = 0.06) and high gene flow (Nm = 3.92) resulted within the GB area. Genetic differentiation was higher between the two areas (Φst = 0.37, Gst = 0.22). Evidence of inbreeding (s = 0.61) was found in the GB area. Conclusions – Inter-annual differences in timing of full flowering phenophase seem to be related chiefly to spring temperatures. The estimates of genetic diversity in S. hispanicum are comparable to those of autogamous and clonal species, while the partitioning of genetic diversity reflects the low structure typical of outcrossing species. Intra-annual flowering synchrony is likely to promote sexual reproduction. Sedum hispanicum seems to adopt multiple reproductive modes to overcome environmental extremes of gypsum outcrops. Key words – Stonecrop, Natura 2000, Gypsum Vein, Northern Apennine, flowering phenology, synchrony, ISSR, genetic variation.